On Fri, 22 Jan 2021 at 18:44, Mark Brown [off-list ref] wrote:

On Thu, Jan 21, 2021 at 12:54:52PM -0600, Josh Poimboeuf wrote:

quoted

2) The shadow stack idea sounds promising -- how hard would it be to
   make a prototype reliable unwinder?

In theory it doesn't look too hard and I can't see a particular reason
not to try doing this - there's going to be edge cases but hopefully for
reliable stack trace they're all in areas where we would be happy to
just decide the stack isn't reliable anyway, things like nesting which
allocates separate shadow stacks for each nested level for example.
I'll take a look.

This reminds me - a while ago, I had a stab at writing a rudimentary
GCC plugin that pushes/pops return addresses to a shadow call stack
pointed to by x18 [0]
I am by no means suggesting that we should rely on a GCC plugin for
this, only that it does seem rather straight-forward for the compiler
to manage a stack with return addresses like that (although the devil
is probably in the details, as usual)

[0] https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=arm64-scs-gcc

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